Production intervals of a wellbore may be uncased to expose porosity and facilitate inflow of hydrocarbon to the wellbore. Hydraulic fracturing may be used to extend fractures from the wellbore into the surrounding formation, facilitating inflow of hydrocarbons. Hydraulic fracturing may have particular use in consolidated reservoirs, where porosity may be decreased relative to other reservoirs. The online Schlumberger oilfield glossary defines “consolidated” as follows: “1. adj. [Geology]: Pertaining to sediments that have been compacted and cemented to the degree that they become coherent, relatively solid rock. Typical consequences of consolidation include an increase in density and acoustic velocity, and a decrease in porosity.”
A straddle packer system is a retrievable system run on coil or standard tubing. Mechanically and hydraulically deployed packers are run in to the wellbore to isolate an interval between two packers. A ported burst sub may be present within the interval. A fracture is initiated within the interval.
A stack frac system uses several pairs of packers to isolate several intervals. A ball drop or dart drop sub is placed between pairs of packers. The packers are set prior to hydraulic fracturing, and balls are dropped one at a time to open frac port subs to initiate and propagate each isolated interval.
A drawback of the straddle packer system and the stack frac system is that a fracture may be initiated at a packer, or may jump past a packer, resulting in loss of isolation of an interval. Once isolation is lost, a fracture in a selected interval will be in communication with a subsequent interval, complicating or preventing initiation of a fracture in the subsequent interval.
The above methods facilitate fractures and propagation of an area of the wellbore, but loss of isolation between intervals may leave a portion of the wellbore without fractures, which may result in lowered production of hydrocarbons from the formation.
It is, therefore, desirable to provide a method of fracturing in an interval between packers that does not result in loss of isolation of the interval.